Reduction of endoscope high frequency leakage current using a common-mode choke

ABSTRACT

An endoscope includes a body and a circuit board mounted within the body. A cable couples the circuit board to an imaging system. A common-mode choke is mounted within the body and is configured to electrically isolate the cable from the body at cautery frequencies. A method includes twisting a plurality of wires together to form a twisted set of wires. The twisted set of wires is wound around a core so that windings do not overlap, and so that a first winding and a last winding are separated from each other. Wires in the twisted set of wires are coupled to a plurality of wires in the cable. Also, these wires in the twisted set of wires are also coupled to the circuit board.

RELATED APPLICATIONS

This patent application claims priority to and the benefit of the filingdate of U.S. Provisional Patent Application 62/289,446, entitled“REDUCTION OF ENDOSCOPE HIGH FREQUENCY LEAKAGE CURRENT USING ACOMMON-MODE CHOKE” filed Feb. 1, 2016, which is incorporated byreference herein in its entirety.

BACKGROUND Field of the Invention

The present invention relates generally to endoscopes forcomputer-assisted surgical system, and more particularly to minimizingunwanted cautery high frequency leakage current flow into the metalshaft of an endoscope.

Description of Related Art

Referring to FIG. 1, surgical system 100 is a computer assisted surgicalsystem that includes an endoscopic imaging system 192, a surgeon'sconsole 194 (master), and a patient side support system 110 (slave), allinterconnected by wired (electrical or optical) or wireless connections196. One or more electronic data processors may be variously located inthese main components to provide system functionality. Examples aredisclosed in U.S. Patent Application Publication No. US 2008/0065105 A1,which is incorporated by reference herein.

Patient side support system 110 includes an entry guide manipulator 130,which may also be called an actively controlled manipulator arm assembly130. At least one surgical device assembly is coupled to entry guidemanipulator 130. Each surgical device assembly includes an instrumenthaving either a surgical instrument or an image capture unit. Forexample, in FIG. 1, one surgical device assembly includes an instrument135-1 with a shaft 137-1 and an image capture unit that extends throughentry guide 115 during a surgical procedure. Instrument 135-1 issometimes referred to an endoscope, or alternatively as an imagingsystem device or camera instrument. Typically, entry guide 115 includesa plurality of channels.

Imaging system 192 performs image processing functions on, e.g.,captured endoscopic imaging data of the surgical site and/orpreoperative or real time image data from other imaging systems externalto the patient. Imaging system 192 outputs processed image data (e.g.,images of the surgical site, as well as relevant control and patientinformation) to a surgeon at surgeon's console 194. In some aspects, theprocessed image data is output to an optional external monitor visibleto other operating room personnel or to one or more locations remotefrom the operating room (e.g., a surgeon at another location may monitorthe video; live feed video may be used for training; etc.).

Surgeon's console 194 includes multiple degrees-of-freedom (“DOF”)mechanical input devices (“masters”) that allow the surgeon tomanipulate the instruments, entry guide(s), and imaging system devices,which are collectively referred to as slaves. These input devices may insome aspects provide haptic feedback from the instruments and surgicaldevice assembly components to the surgeon. Surgeon's console 194 alsoincludes a stereoscopic video output display positioned such that imageson the display are generally focused at a distance that corresponds tothe surgeon's hands working behind/below the display screen. Theseaspects are discussed more fully in U.S. Pat. No. 6,671,581, which isincorporated by reference herein.

Control during insertion of the instruments may be accomplished, forexample, by the surgeon moving the instruments presented in the imagewith one or both of the masters; the surgeon uses the masters to movethe instrument in the image side to side and to pull the instrumenttowards the surgeon. The motion of the masters commands the imagingsystem and an associated surgical device assembly to steer towards afixed center point on the output display and to advance inside thepatient.

In one aspect, the camera control is designed to give the impressionthat the masters are fixed to the image so that the image moves in thesame direction that the master handles are moved. This design causes themasters to be in the correct location to control the instruments whenthe surgeon exits from camera control, and consequently this designavoids the need to clutch (disengage), move, and declutch (engage) themasters back into position prior to beginning or resuming instrumentcontrol.

Base 101 of patient side support system 110 supports an arm assemblythat includes a passive, uncontrolled setup arm assembly 120 and anactively controlled manipulator arm assembly 130. Actively controlledmanipulator arm assembly 130 is sometimes referred to as entry guidemanipulator 130. An entry guide manipulator assembly platform 132,sometimes referred to as platform 132, is coupled to a distal end offourth manipulator link 119. An entry guide manipulator assembly 133 isrotatably mounted on platform 132. Arrow 190 shows the distal andproximal directions.

Entry guide manipulator assembly 133 includes an instrument manipulatorpositioning system. Entry guide manipulator assembly 133 rotates aplurality of instrument manipulator assemblies 140-1, 140-2 as a grouparound axis 125.

Each of a plurality of instrument manipulator assemblies 140-1, 14-2 iscoupled to entry guide manipulator assembly 133 by a different insertionassembly 136. In one aspect, each insertion assembly 136 is atelescoping assembly that moves the corresponding instrument manipulatoraway from and towards entry guide manipulator assembly 135. In FIG. 1,each of the insertion assemblies is in a fully retracted position.

Each of the plurality of instrument manipulator assemblies 140-1, 140-2includes a plurality of motors that drive a plurality of outputs in anoutput interface of that instrument manipulator. See U.S. PatentApplication No. 61/866,115 (filed on 15 Aug. 2013), which isincorporated by reference, for one example of an instrument manipulatorand a surgical instrument that can be coupled to the instrumentmanipulator.

Each of plurality of surgical device assemblies 180 includes a differentof the plurality of instrument manipulator assemblies and one of asurgical instrument and an image capture unit. Each of instruments135-1, 135-2 includes a body that houses a transmission unit. Thetransmission unit includes an input interface including a plurality ofinputs. Each of instruments 135-1, 135-2 also includes a shaft 137-1,137-2 sometimes referred to as a main tube that extends in the distaldirection from the body. An end effector is coupled to a distal end ofthe shaft of a surgical instrument assembly, and an image capture unit,e.g., a camera, is included in a distal end of a different surgicalinstrument assembly. See U.S. Patent Application No. 61/866,115 (filedon 15 Aug. 2013), which is incorporated by reference, for one example ofan instrument manipulator assembly and a surgical instrument.

Each of instruments 135-1, 135-2 is coupled to the instrument mountinterface of a corresponding instrument manipulator assembly 140-1,140-2 so that a plurality of inputs in an input interface of thetransmission unit in instrument 135-1, 135-2 are driven by plurality ofoutputs in the instrument mount interface of instrument manipulatorassembly 140-1, 140-2. See U.S. Patent Application No. 61/866,115 (filedon 15 Aug. 2013).

As shown in FIG. 1, the shafts of plurality of surgical deviceassemblies 180 extend distally from bodies of the instruments. Theshafts extend through a cannula 116 placed at the entry port into thepatient (e.g., through the body wall or at a natural orifice). In oneaspect, an entry guide 115 is positioned within cannula 116, and eachinstrument shaft extends through a channel in entry guide 115, so as toprovide additional support for the instrument shafts.

SUMMARY

A surgical system includes an endoscope and a cable connecting theendoscope to an imaging system. The cable including a first plurality ofwires. The endoscope includes a body, a circuit board mounted within thebody, and a common-mode choke mounted within the body. The common-modechoke is coupled to the first plurality of wires and is coupled to thecircuit board.

The cable includes a shield that encloses, e.g., surrounds, the firstplurality of wires. The shield is connected to the common-mode choke sothat the common-mode choke electrically isolates the cable shield fromthe body of the endoscope.

In one aspect, the common-mode choke includes a second plurality ofwires. The second plurality of wires includes a first end, a second end,and a portion between the first end and the second end. The portion ofthe second plurality of wires between the first end and the second endis wound around the core in non-overlapping windings and is wound sothat the first end and the second end are separated from one another.Some of the wires of the second plurality of wires are coupled to thefirst plurality of wires and to the circuit board. In one aspect, thesecond plurality of wires are twisted together prior to being woundaround the core.

In one aspect, the core of the common-mode choke is a gapless core. Thegapless core is, for example, a nano-crystalline ferrite core.

In another aspect, the endoscope includes an electrical optical couplercoupled to common-mode choke and coupled to the circuit board.

In still another aspect, a method includes reducing common-mode currentinduced on a cable of an endoscope by coupling a common-mode chokebetween the cable and a circuit within the endoscope.

In yet another aspect, a method includes twisting a plurality of wirestogether to form a twisted set of wires. The twisted set of wires iswrapped around a core so that windings do not overlap, and so that afirst winding and a last winding are separated from each other. One ormore of the wires in the twisted set of wires are coupled to one or morewires in a plurality of wires of a cable of an endoscope. The one ormore wires in the twisted set of wires are also coupled to a circuitboard. A shield of the cable is connected to one wire of the twisted setof wires. The one wire being different from the one or wires in thetwisted set of wires.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a prior-art computer-assisted surgicalsystem.

FIG. 2 is an illustration of an endoscope connected to a cable with acommon-mode choke connecting the cable to the circuit board in theendoscope.

FIG. 3A is an illustration of one aspect of the common-mode choke.

FIG. 3B is a schematic diagram of the common-mode choke.

FIGS. 4A and 4B are each an illustration of another endoscope connectedto a cable with a combination of a common-mode choke and an electricaloptical coupler.

In the drawings, the first digit of a three digit reference numeral isthe figure number in which the element having that reference numeralfirst appeared.

DETAILED DESCRIPTION

In surgical system 100, typically a cable runs between endoscope 135-1and imaging system 192. The cable has a significant capacitance toground. When one of the instruments in surgical system 100 includes oris an energized cautery tool, the cautery tool's energy source provideshigh frequency energy with the main energy being located in the 400 kHzto 500 kHz range and with harmonics up to the 4 MHz range. The cauterytool energy source can unintentionally supply energy to any object thathas a path to ground (earth) by a direct wired connection or bycapacitive coupling. The cautery tool energy source can source thisenergy from either of its two output leads: (1) the High Voltage leadwhich connects to the cautery tool or (2) the Patient Return leadnormally connected to the patient's body.

The cautery tool energy source can drive current into the endoscope'smetal shaft 137-1 by virtue of the shaft being electrically connected tothe cable which has a large capacitance to earth. The current can travelby two paths: (1) from the cautery tool energy source High Voltage leadbeing capacitively coupled (wrapped around) the endoscope cable, or (2)from patient's body (which is connected to the Patient Return lead)touching the endoscope shaft. During cautery activation unintendedcurrent flow may cause arcing at the patient-tissue-endoscope-shaftinterface. An arc at the patient's tissue, may burn the tissue, and ofcourse is undesirable.

Endoscope 200 (FIG. 2) reduces the unintended current flow by insertinga high impedance component 215 (which may be high impedance at allsignal frequencies, or only within a range of frequencies such as atcautery frequencies) between the endoscope body, e.g., housing 201(sometimes referred to as body 201), and the large capacitance to groundof cable 205. This high impedance component 215 may also be called acommon-mode choke 215. Cable 205 connects endoscope 200 to imagingsystem 292. Imaging system 292 is equivalent to imaging system 192. Atthe same time, in various embodiments, component 215 must not have ahigh impedance for the data and power wires of cable 205. In one aspect,this component is a common-mode choke 215. The data and power aredifferential signals (traveling down one wire and returning on itcompanion ground wire, whereas the cautery current tries to travel incommon down all the wires). Common-mode choke 215 behaves as a highimpedance for common-mode currents and as a low impedance fordifferential currents.

Common-mode choke 215 is included within housing 201 of endoscope 200.Common-mode choke 215 is connected between cable 205 and a circuit board210 and connected between a shield of cable 205 and housing 201,sometimes referred to as body 201. In one aspect, common-mode choke 215is mounted on circuit board 210. Common-mode choke 215 has an inductancein the tens of millihenries, e.g., 30 millihenries in one aspect, and soattenuates any common-mode current on cable 205 by over a factor ofthree. This attenuation is sufficient to reduce the common-mode cauterycurrent to levels accepted by international standards. Common-mode choke215 has minimal stray capacitance between its input and output leads.The signal coupling between parallel windings of common-mode choke 215is small enough that signal integrity is not compromised.

In one aspect, endoscope 200 includes a plurality of image capture unitsin the distal end of main tube 202. An illuminator in endoscope 200provides light to the distal end of main tube 202. Arrow 290 defines theproximal direction and the distal direction in FIGS. 2, 4A, and 4B.

The circuits included within housing 201 of endoscope 200 that power theilluminator and the image capture units, move data from the imagecapture units to imaging system 292, etc. are represented by circuitboard 210. Circuit board 210, in some instances, may be implemented bymore than one circuit board. Circuit board 210 is coupled to units inthe distal end of main tube by a cable 203. There may be other cablesthat run from circuit board 210 to other elements housed within housing201. The size and shape of housing 201 is fixed by the need forendoscope 200 to be in close proximity to other instruments, as shown inFIG. 1, and to not collide with the other instruments or inhibit therange of motion of the other instruments.

Cable 205 includes, in one aspect, a power line, a ground line, signallines, and a shield that encloses these lines. The power line, groundline, and signal lines together are sometimes referred to as a firstplurality of wires. Thus, in this aspect, the first plurality of wiresis encased in a shield. Cable 205 is connected to housing 201. However,in connecting cable 205 to housing 201, neither the shield nor any ofthe wires in cable 205 are permitted to contact housing 201.

Common-mode choke 215 is connected to the first plurality of wires and,in this aspect, is connected to circuit board 210, i.e., is connectedbetween cable 205 and circuit board 210. The shield of cable 205 is alsoconnected thru common-mode choke 215 to a ground 204 on housing 201. Theshield of cable 205 is electrically isolated from housing 201 ofendoscope 200 by common-mode choke 215, and the shield does not touchany electrically conductive part that is connected to housing 201.

Common-mode choke 215 includes a plurality of non-overlapping windings.A beginning winding in the plurality of non-overlapping windings isseparated from an ending winding of the plurality of non-overlappingwindings. Since the windings of common-mode choke 215 do not overlap andthe beginning winding is separated from the ending winding, there isminimal capacitance across the input and output leads of common-modechoke 215. In this aspect, the core of common-mode choke 215 does nothave an opening and is selected to have the highest AL-value (number ofmillihenries per turn) possible for the size of the core.

FIG. 3A is an illustration of common-choke 315, an embodiment ofcommon-mode choke 215. FIG. 3B is a schematic diagram of common-modechoke 315. In this aspect, cable 205 includes a ground line, a powerline, four signal lines and the shield surrounding these lines. Aftercable 205 enters housing 201, the ground line and the shield are twistedtogether so that there are six lines, a shield and ground linecombination, a power line, and four signal lines.

Common-mode choke 315 includes a second plurality of wires 340, which inthis example, is six wires. Prior to being wound on core 320, secondplurality of wires 340 are twisted together to form a set of twistedwires 330. Set of twisted wires 330 has a first lead 330-1, a secondlead 330-2, and a portion between first lead 330-1 and second lead330-2. Similarly, each wire of the second plurality of wires 340 has afirst end 340-1, a second end 340-2 and a portion between first end340-1 and second end 340-2.

Set of twisted wires 330, sometime referred to as wires 330, are woundaround core 320 so that the windings do not overlap. Avoiding overlap ofthe windings has several advantages. There is minimal capacitancecreated between winding, and this helps to minimize the input-to-outputcapacitance of common-mode choke 315.

Since there are no overlapping windings, there is no concern aboutarcing between overlapping windings due to insulation failure. In oneaspect, the common-mode voltage is about 3000 volts, and, in thisaspect, common-mode choke 315 has 28 windings. Thus, each winding dropsaround 107 volts, which is well within the capability of conventionalwire insulation. Thus, the non-overlapping windings eliminate anyconcern about the insulation on wires 330 failing.

A first winding 331, a beginning winding, around core 320 is separatedby a gap 321 from a last winding 332, an ending winding, around core320. Gap 321 separates input lead 330-1, a first lead, from output lead330-2, a second lead, which also helps to minimize the capacitance ofcommon-mode choke 315 and also helps to prevent arching between thefirst lead and second lead. As shown in FIG. 3A, the windings aroundcore 320 have a letter “C” shape, where gap 321 in the windings is theopening in the letter “C” shape. The size of gap 321 is selected so thatthere is no possibility of arcing between input lead 330-1 and outputlead 330-2.

Core 320 is a ferrite toroid core or a ferrite bobbin/pot core. In oneaspect, core 320 is a nano-crystalline ferrite core without a gap. Thiscore material provides a much higher inductance per turn compared toother core materials, which results in less stray capacitance from inputlead 330-1 to output lead 330-2. In one aspect, core 320 is anano-crystalline ferrite core in a plastic casing. This core hasproperties such as those in Table 1.

TABLE 1 Nominal Core Dimensions Outer Diameter 16 mm Inner Diameter 10mm Height 6 mm Iron Cross Section A_(Fe) 0.14 cm² AL  10 KHz 43.0 μH 100kHz 10.1 μH Saturation Current I_(cm)  10 KHz 0.3 A 100 kHz 0.6 A

A core having these properties is commercially available fromVacuumschmelze GMBH & Co., Gruner Weg 37, D 63450 Hanau, Germany underPart No. T6006-L2016-W403. While the dimensions of the core are given inTable 1, the cross sectional area of the core is a key factor in settingthe maximum current the core can handle before the core saturates (wherethe inductance droops to a lower value). Another core choice withdifferent dimensions is just as effective if that core has approximatelythe same AL value and cross-sectional area.

Each of the six wires in the twisted set of wires in input lead 330-1 ofcommon-mode choke 315 are either connected to (FIGS. 2 and 4A) or arecoupled to (FIG. 4B) a different one of the six wires (a shield andground line combination, a power line, and four signal lines) of cable205. Thus, each of the six wires—an example of a plurality of wires—inthe twisted set of wires in input lead 330-1 are coupled to a differentone of the six wires (a shield and ground line combination, a powerline, and four signal lines) of cable 205.

One of the six wires in the twisted set of wires in output lead 330-2 ofcommon-mode choke 315—the one coupled to the a shield and ground linecombination of cable 205—is connected to a ground 204. The other wiresin the six wires in the twisted set of wires in output lead 330-2 ofcommon-mode choke 315 are coupled to circuit board 210.

While in this aspect, a gapless nano-crystalline ferrite is used, inother aspects, a gapless ferrite core could be used if the performancecharacteristics of the gapless ferrite core are acceptable for thecommon mode currents encountered during a surgical procedure and ifthere is space for the resulting common-mode choke within theinstrument. Similarly, a gapped ferrite core could be used if theperformance characteristics of the gapped ferrite core are acceptablefor the common mode currents encountered during a surgical procedure andif there is space for the resulting common-mode choke within theinstrument.

Electrical optical couplers have been considered in electricallyisolating cable 205 from housing 201 of endoscope 400A. Typically, anelectrical optical coupler functions properly so long as the common-modevoltages are less than about 25,000 volts/microsecond. With an arcingcautery instrument, a typical voltage is 3000 volts, and the rise timeof the arc is on the order of five to ten nanoseconds, which results inabout 500,000 volts/microsecond. Hence, an electrical optical coupleralone would not work properly in the presence of common-mode voltagesgenerated by an arcing cautery instrument. However, a common-mode chokecombined with an electrical optical coupler attenuates the common-modevoltage so that the electrical optical coupler works properly.

FIGS. 4A and 4B illustrate two equivalent ways of utilizing acommon-mode choke with an optical coupler. In FIG. 4A, common-mode choke415A is inserted between an electrical optical coupler 416A on circuitboard 210A and cable 205. In one aspect, common mode choke 415A is alsomounted on circuit board 210A. In FIG. 4B, electrical optical coupler416B is on a circuit board 410 and cable 205 is connected to opticalcoupler 416B. Common mode choke 415B is connected between electricaloptical coupler 416B and circuit board 210.

Common-mode chokes 415A and 415B are constructed in a way that isequivalent to the way that common-mode choke 215 was constructed, exceptcommon-mode chokes 415A and 415B are each smaller than common-mode choke215. While common-mode choke 215 has an inductance in the tens ofmillihenries, each of common-mode chokes 415A and 415B has an inductanceof about 100 microhenries. This means that a smaller core and a smallernumber of windings can be used. However, the windings still do notoverlap and the first winding is separated from the last winding so thatthe windings have the letter “C” shape. The other aspects of common-modechokes 415A and 415B are the same as common-mode choke 215, and so arenot repeated here.

As used herein, “first,” “second,” “third,” etc. are adjectives used todistinguish between different components or elements. Thus, “first,”“second,” and “third” are not intended to imply any ordering of thecomponents or elements or to imply any total number of components orelements.

The above description and the accompanying drawings that illustrateaspects and embodiments of the present inventions should not be taken aslimiting—the claims define the protected inventions. Various mechanical,compositional, structural, electrical, and operational changes may bemade without departing from the spirit and scope of this description andthe claims. In some instances, well-known circuits, structures, andtechniques have not been shown or described in detail to avoid obscuringthe invention.

Further, this description's terminology is not intended to limit theinvention. For example, spatially relative terms—such as “beneath”,“below”, “lower”, “above”, “upper”, “proximal”, “distal”, and thelike—may be used to describe one element's or feature's relationship toanother element or feature as illustrated in the figures. Thesespatially relative terms are intended to encompass different positions(i.e., locations) and orientations (i.e., rotational placements) of thedevice in use or operation in addition to the position and orientationshown in the figures. For example, if the device in the figures wereturned over, elements described as “below” or “beneath” other elementsor features would then be “above” or “over” the other elements orfeatures. Thus, the exemplary term “below” can encompass both positionsand orientations of above and below. The device may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein interpreted accordingly. Likewise,descriptions of movement along and around various axes include variousspecial device positions and orientations.

The singular forms “a”, “an”, and “the” are intended to include theplural forms as well, unless the context indicates otherwise. The terms“comprises”, “comprising”, “includes”, and the like specify the presenceof stated features, steps, operations, elements, and/or components butdo not preclude the presence or addition of one or more other features,steps, operations, elements, components, and/or groups. Componentsdescribed as coupled may be electrically or mechanically directlycoupled, or they may be indirectly coupled via one or more intermediatecomponents.

All examples and illustrative references are non-limiting and should notbe used to limit the claims to specific implementations and embodimentsdescribed herein and their equivalents. Any headings are solely forformatting and should not be used to limit the subject matter in anyway, because text under one heading may cross reference or apply to textunder one or more headings. Finally, in view of this disclosure,particular features described in relation to one aspect or embodimentmay be applied to other disclosed aspects or embodiments of theinvention, even though not specifically shown in the drawings ordescribed in the text.

Embodiments described above illustrate but do not limit the disclosure.It should also be understood that numerous modifications and variationsare possible in accordance with the principles of the presentdisclosure. For example, in many aspects the devices described hereinare used as single-port devices; i.e., all components necessary tocomplete a surgical procedure enter the body via a single entry port. Insome aspects, however, multiple devices and ports may be used.

1. An imaging apparatus comprising: a cable, an imaging system, and anendoscope; the cable being configured to be connected to the imagingsystem and to the endoscope; the cable including a first plurality ofwires; and the endoscope being configured to be connected to the cable,the endoscope comprising: a body; a circuit board mounted within thebody; and a common-mode choke mounted in the body, the common-mode chokebeing coupled to the first plurality of wires and being coupled to thecircuit board.
 2. The apparatus of claim 1, the cable further comprisinga shield, the first plurality of wires being enclosed in the shield, theshield being connected to the common-mode choke and being electricallyisolated from the body by the common-mode choke.
 3. The apparatus ofclaim 1, the common-mode choke having a first winding and a lastwinding, the first winding not overlapping with and separated from thelast winding.
 4. The apparatus of claim 1, the common-mode choke havinga plurality of non-overlapping windings.
 5. The apparatus of claim 4,the plurality of non-overlapping windings including a first winding anda last winding, the first winding not overlapping with and separatedfrom the last winding.
 6. The apparatus of claim 1, the common-modechoke having a second plurality of wires and a core, the secondplurality of wires having a first end and a second end, a portion of thesecond plurality of wires between the first end and second end beingwound around the core in non-overlapping windings and being wound sothat the first end and the second end are separated from one another,wherein wires of the second plurality of wires are coupled to the firstplurality of wires and to the circuit board.
 7. The apparatus of claim6, the second plurality of wires being twisted together prior to beingwound around the core.
 8. The apparatus of claim 6, the cable furthercomprising a shield, the first plurality of wires being enclosed in theshield, the shield being coupled to a wire of the second plurality ofwires.
 9. The apparatus of claim 6, the core being a gapless core. 10.The apparatus of claim 9, the core being a nano-crystalline ferritecore.
 11. The apparatus of claim 6, the core being a nano-crystallineferrite core.
 12. The apparatus of claim 1, the endoscope furthercomprising an electrical optical coupler coupled to the cable andcoupled to the common-mode choke.
 13. A method of operating an imagingsystem, the method comprising: reducing common-mode current induced on acable connected between an imaging system and an endoscope by utilizinga common-mode choke between the cable and a circuit within theendoscope, the common-mode choke being mounted within a body of theendoscope.
 14. The method of claim 13 further comprising: shielding afirst plurality of wires of the cable with a shield enclosing the firstplurality of wires, wherein the shield is connected to the common-modechoke and is electrically isolated from the body by the common-modechoke.
 15. A method comprising: twisting a plurality of wires togetherto form a twisted set of wires; wrapping the twisted set of wires arounda core so that resulting wire windings do not overlap, and so that afirst winding and a last winding are separated from each other; couplingone or more wires of the twisted set of wires to one or more wires of asecond plurality of wires, the second plurality of wires being in acable for an endoscope; and coupling the one or more wires of thetwisted set of wires to a circuit board.
 16. The method of claim 15,further comprising: coupling a shield of the cable to a wire of thetwisted set of wires, the wire of the twisted set of wires beingdifferent from the one or more wires coupled to the one or more wires ofthe twisted set of wires.
 17. The method of claim 15, furthercomprising: coupling an electrical optical coupler coupled to the cable;and coupling the electrical optical coupler to the second plurality ofwires.
 18. The apparatus of claim 6, wherein the core is a gapless,nano-crystalline ferrite core.